feat: shard modules and API integration tests (#6775)

what:

- runs module and api integration tests in matrix strategy
  - v28 of jest comes with sharding support, which we can utilize when we upgrade
- splits the tests by number of matrix jobs and run them in parallel
  - This introduced some flakiness in some specs, but couldn't reproduce locally. Those have been skipped for now.
- uses swc/jest for added performance
  - Locally, a chunk took 90 seconds with babel and 30 seconds with swc. 
  - This translated to 2 mins saved per shard in CI, but haven't tested this enough.

integration-tests/jest.config.js

@@ -25,7 +25,7 @@ module.exports = {
     `__testfixtures__`,
     `.cache`,
   ],
-  transform: { "^.+\\.[jt]s$": `<rootDir>/jest-transformer.js` },
+  transform: { "^.+\\.[jt]s$": ["@swc/jest"] },
   setupFiles: ["<rootDir>/integration-tests/setup-env.js"],
   setupFilesAfterEnv: ["<rootDir>/integration-tests/setup.js"],
 }